In recent years many low power mobile devices have come into use. In many cases these devices use a battery to provide electric power, in other cases they draw their power from another device such as a computer (through a USB port for example). Many of these devices are also used to transmit and receive data. Devices that use the Bluetooth protocol are good examples of such devices.
One of the most common drawbacks of such devices is the need for recharge of the battery (in the case of a rechargeable battery) or replacement of the battery (in the case of a non rechargeable battery). Another drawback of such devices, if they are such as to transmit and receive data, is the requirement to transmit data in all directions, to ensure that it will be picked up by the base station, which increases power consumption significantly, as well as increasing any health risks associated with electromagnetic transmissions.
It would be desirable if such devices were able to receive their power, or at least part of it, wirelessly from a remote source, thus reducing the need for recharge cycles or change of batteries. It would also be useful if such devices were able to transmit data directly to the receiver without wasting significant amounts of energy on transmitting it in unwanted directions.
There are shown in the prior art methods of transmitting power through free space without the need for wires. Initial attempts were made by Tesla in the late 19 century. Tesla was able to operate an electric lamp located 25 miles from the power source in Colorado. Tesla induced alternating current to the earth and used a wire to collect the generated AC current and operate a lamp. His invention is described in U.S. Pat. No. 649,621, U.S. Pat. No. 685,593, U.S. Pat. No. 685,954, U.S. Pat. No. 514,168, U.S. Pat. No. 593,138, U.S. Pat. No. 685,955, U.S. Pat. No. 685,956, U.S. Pat. No. 685,957, U.S. Pat. No. 685,958, U.S. Pat. No. 787,412, U.S. Pat. No. 1,119,732
In the beginning of the 20th century Yagi in Japan transmitted power using Yagi-Uda antennas making the transmission of power essentially directional. The beam from the Yagi-Uda antenna widens with distance from the antenna reducing the yield of transmission. Yagi's invention is described in various articles. Today other solutions to the problem are attempted. One such example is shown in European patent document No. EP 0734110, for Wireless Power Transmission, to M. Stasys, in which is described the use of a laser or other type of directional energy beam, to transmit power down the beam path from a power source, such as an overhead conductor, to a load, such as an electric tram. This system has some disadvantages. Firstly, if the beam is blocked the radiation continues, in the case of a high energy beam health risk and potential damage to objects crossing the beam's path pose a significant limitation on the use of such a device. Furthermore if a mobile receiver is to be used, a servo mechanism to direct the beam towards the receiver may be needed. There are two significant problems associated with such a servo mechanism, first, it can fail, directing the beam into unwanted places, second it complicates the transmitter and adds to its price.
In U.S. Pat. No. 6,798,716 Charych teaches the use of directional ultrasound for transmission of power. As with the Yagi-Uda antenna the ultrasound beam may require a servo mechanism to direct it to the receiver and the efficiency of the transmission could drop with distance.
Even more recently Cheng et al showed transmission of power using electrical induction (U.S. Pat. No. 6,906,495). Typically the use of such a system would be to transmit energy over very short distances measured in mm and centimeters. Should the same principle be used to transmit power over larger distances, two problems may be encountered, first the efficiency of transmission may drop significantly and second, if a mobile receiver is to be used, a servo mechanism with its associated risks and price may have to be added to the device.
In most of the above methods, the transmitter can transmit power in directions where there is no receiver, the generated radiation may be harmful, especially if it is not blocked by the receiver or if the servo mechanism fails to direct it there. Although servo systems are not described in most of the above systems, should it be used to provide power to a mobile unit, such as a mobile cellular telephone, the beam generated will have to be directed exactly at the receiver.
The receiver too can be equipped with a similar servo mechanism in order to direct the data beam back to the transmitter. However such a mechanism has a number of drawbacks: It has moving parts that may fail over time, with possibly reduced reliability. It can, in error, or due to a fault of the system, hit an object sensitive to the energy beam (such as a human eye) and cause harm to it. Power may be lost due to imperfect direction of the beam, causing inefficiency and further possible damage to the surroundings. It would also be difficult, using a single laser, or an ultrasound or microwave beam, to transmit power to more than one device. Lastly, a directional beam which has no fool proof mechanism to stop it in case the beam is blocked cannot transmit large amounts of power and still meet safety requirements.
Another method to provide wireless power transmission is to have the transmitter transmit energy in all directions, such as by putting a very strong lamp in a room and using a photovoltaic cell to convert the energy to electrical power. However it is the nature of such an isotropic or pseudo-isotropic method of propagating radiation, that the power falls off very quickly with distance, so the power consumption of such a transmitter would need to be high or the range limited. Another drawback of such an approach is the various health hazards and inconveniences.
Therefore, it would be useful to have a combination of a receiver and transmitter for transmitting power and transmitting and receiving data without the need for connecting wires, that overcomes at least some of the disadvantages of the prior art, in that it:
(i) directs a significant amount of the energy transmitted from the transmitter towards the receiver, without need for moving parts, in a situation where the receiver may be able to move around the reception volume;
(ii) has built-in safety features that will turn off the directional transmitted energy beam quickly when it is blocked; and
(iii) is able to send data from the mobile side to the energy transmitter in an energy efficient way.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.